The present invention is generally related to absorbent cores of absorbent articles where the absorbent core is formed from one continuous piece of material and where the absorbent core has elastic properties at low tensions.
Absorbent articles are used for a variety of applications including disposable diapers, training pants, disposable swim pants, adult incontinence garments, feminine hygiene products, wound dressings and nursing pads. The xe2x80x9cworkhorsexe2x80x9d of an absorbent article is the absorbent core, which is the portion of the article that collects and retains a targeted exudate. This workhorse component can be thick and bulky relative to the other components of the article. Consequently, the absorbent core can reduce the flexibility and conformability of the article, thereby compromising the fit of the article on or against a wearer. xe2x80x9cGoodxe2x80x9d fit is generally understood to correlate with good performance of the absorbent article.
The absorbent cores of the invention overcome deficiencies associated with known absorbent cores. Technical advances and the resulting improvements in the materials available for use in absorbent articles have led to better-fitting absorbent articles. For example, many years ago leg elastics were introduced to disposable diapers to improve the fit of the diaper around the legs of the wearer and to have a gasketing effect. Subsequently, extensibility and elasticity have been proposed for other components of disposable diapers and other absorbent articles. Not to be overlooked, various constructions and designs have been proposed for making the absorbent core extensible or elastic. Depending on the overall configuration or construction of an absorbent article, it can be beneficial to incorporate xe2x80x9cstretchxe2x80x9d into the absorbent core. Benefits include improvement of overall fit provided by virtue of the bulkiest component being more flexible and by virtue of not inhibiting any stretch or flexibility that may be possessed by other components of the absorbent article.
Generally speaking, when a material is xe2x80x9cextensiblexe2x80x9d, it is understood that the length or another dimension of the material can be increased with application of a force. The same can be said about a material that is described as being xe2x80x9celasticxe2x80x9d. The fundamental difference between xe2x80x9cextensibilityxe2x80x9d and xe2x80x9celasticityxe2x80x9d is the degree to which the material retracts once the force causing increase in length or other dimension is released. Extensible materials do not return to their original length or dimension as much as elastic materials. Extensible and elastic materials can be selected for almost every component of an absorbent article, including the absorbent core. Various considerations go into selecting such materials for a particular absorbent article design: the magnitude of elongation that the material is capable of; the force required to achieve that magnitude of elongation; the magnitude of retraction experienced by the material upon removal of the force and the speed with which the material retracts. Once the materials are selected for each component of the absorbent article, the materials must all work together to provide an article that is easy to apply, fits comfortably and performs its intended function.
The materials used to form the components of absorbent articles can be made extensible or elastic by building extension-capacity into the material (such as by necking or creping) or by incorporating an elastic material (such as LYCRA elastic strands) into the material. The actual components of an absorbent article (e.g. the outer cover, the liner, the containment flaps etc.) can also be made extensible or elastic by building extension-capacity into the component (such as by pleating or segmentation) or by incorporating an elastic material into the component. Generally speaking, materials and components are selected and designed to readily provide elongation or stretch without application of much force. Otherwise, the absorbent article would be difficult to use or uncomfortable to wear.
Attempts have been made to build extensibility or elasticity into the absorbent cores of absorbent articles. Those attempts have included both the building-in of extension capability and the incorporation of elastic materials. One way to xe2x80x9cbuild-inxe2x80x9d extension capability is to break the typical length of the absorbent core down into free-moving segments. A segmented absorbent core will typically have greater extensibility than a continuous piece or unitary absorbent core. For example, if a unitary absorbent core that is six inches in length is modified to be a segmented absorbent core having six, one inch segments, the segmented absorbent core will have more inherent extensibility that the continuous (six inch long) absorbent core. Broken down into independent-moving increments, the segmented core has increased freedom of movement over a unitary absorbent core; the segmented core can more readily respond to the relative motion of outer cover and liner components that may be extensible or elastic. Despite the advantages provided by the segmented absorbent core, the performance of the absorbent core, vis-à-vis the ability to rapidly distribute and retain fluids, may be compromised. The xe2x80x9cbreaksxe2x80x9d or xe2x80x9cdiscontinuitiesxe2x80x9d between segments of the core may interrupt the wicking of fluids. Consequently, while segmentation is one approach to build-in extensibility or elasticity, segmentation has its drawbacks.
Elasticity has been built-in to absorbent cores through the incorporation of elastic materials into the traditional superabsorbent plus fluff (wood pulp) mixture. For example, elastic materials like LYCRA elastic strands, have been incorporated with superabsorbent and wood pulp to form elastic absorbent cores; the result is an absorbent structure having the ability to extend and retract. In some executions, relatively high quantities of elastic materials (e.g. greater than 30%) have been incorporated into the absorbent structure. While such absorbent cores have definitive elastic properties, it is possible that their absorptive capacity is diminished. Absorptive capacity is potentially diminished because superabsorbent and wood pulp are significantly replaced by elastic materials. A potential outcome is that the absorbent core must be oversized to have an absorptive capacity equal to a non-elastic core; the extra bulk counteracts the benefits of flexibility and conformability provided by an elastic core.
When elasticity is built-in to absorbent cores, it is known that is desirable to have the absorbent core extend at low tension. That is to say, the absorbent core extends or elongates with the application of minimal force (or tension). Typically, the absorbent core of an absorbent article forms the central portion of the article and the other components are built around the absorbent core. If the absorbent core requires the application of a relatively high force to extend it, any extensible or elastic capacity built-in to the other components will be dwarfed. Therefore, it is desirable to have the central and bulkiest component capable of elongating with the application of a relatively low force. In some applications, the absorbent core is capable of elongating under low tension and the absorbent core retracts almost completely (i.e. more than 90%) upon release of the force. While near total retraction is indicative of the elasticity of a component, near complete retraction may not be desirable. The force to elongate an absorbent article or components of an absorbent core is typically applied by the wearer or caregiver during the application of the article. It can be desirable for the article to form some xe2x80x9cmemoryxe2x80x9d of the elongation during application and to not completely or nearly completely retract. Some xe2x80x9csetxe2x80x9d (i.e. less than complete retraction) of the elastic components of the article can be desirable to provide customized fit of the article to an individual wearer. Less than total or near total retraction by the elastic components can also impart a more comfortable fit to the absorbent article because the elastic components are left with some xe2x80x9cgivexe2x80x9d to conform to the shape of the individual wearer. Further, absorbent cores having high retraction may not possess elastic properties that are compatible with the other components of the absorbent article. Elastic absorbent cores that retract disproportionately to the other components of the absorbent article (i.e. the outer cover and liner) can be ill-fitting and have reduced performance. For example, if the absorbent core retracts more than the other components, the article will bunch-up and be uncomfortable to wear.
Ordinarily, the purpose of designing an absorbent core to be extensible or elastic is to create compatibility with other components of the absorbent articles into which extensibility or elasticity has been incorporated. That is, it is desirable for the absorbent core to be elongatable so that the stretch or elongation capability of the other components is not xe2x80x9ctied-upxe2x80x9d or diminished. While it is understood that stretchable materials provide better fitting absorbent articles, improved fit can not be achieved at the cost of a loss in performance. Therefore, it is important for stretchable absorbent cores to have performance at least equivalent to conventional, non-stretch absorbent cores. One aspect of article performance is the integrity of the absorbent core when wet or loaded.
Therefore, there remains a need for a stretchable absorbent core that is continuous so that the distribution and flow of targeted exudates is not inhibited. Further, there remains a need for an absorbent core possessing elastic properties without the significant replacement of absorptive materials within the core. Additionally, there remains a need for an absorbent core capable of elongating upon application of a low force (or tension) with managed retraction so as to not retract disportionately.
The present invention is directed in part to a dynamic-fitting absorbent article that includes a liquid impermeable outer cover, a liquid permeable bodyside liner and a continuous elastic absorbent core. The absorbent articles of the invention are dynamic-fitting to provide a conforming and comfortable fit to the wearer throughout the cycle of use of the absorbent article (i.e. providing a good fit at the time of application, providing a good fit as the article begins to be loaded and providing a good fit after the article has been completely loaded). The bodyside liner is provided in superimposed relation to the outer cover and the absorbent core is disposed between the outer cover and the bodyside liner. In one aspect of the present invention, the continuous elastic absorbent core can extend from about 80 to about 400 percent upon application or experience of a force of from about 60 to about 325 grams. Put differently, the continuous elastic absorbent core can have a tension of from about 60 to about 325 grams when extended by about 80% of its initial length. Additionally, the continuous absorbent core can have the same range of tension when extended by about 100, 200, 300 or 400% of an initial length (or other dimension). More desirably, the continuous elastic absorbent core can extend from about 80 to about 400 percent upon a force of from about 100 to about 250 grams. This is the same as saying that the continuous elastic absorbent core has a tension of from about 100 to about 250 grams when it is extended by 80 percent or any other percentage extension between about 80 and about 400 percent (e.g. 100, 200, 300 or 400 percent).
In another aspect, the continuous elastic absorbent core can recover no more than about 80% of an original dimension upon relaxation of the extension force. That is to say, the elastic absorbent core can retract only to within about 80% of the original dimension after the extension force is removed. Put differently, the post-extension dimension can be about 120% of the original dimension. For example, if the absorbent article (and therefore the absorbent core) is extended or elongated during application of the article, the absorbent core recovers no more than about 80% of its original length and/or width once the absorbent article is fastened or secured to the wearer.
In order to reduce the force or tension needed to fully elongate or extend the absorbent core, the continuous elastic absorbent core of the invention can have a tension reducing geometry in a crotch section of the absorbent core. Typical absorbent cores have an hourglass or rectangular shape that extends between a front waist section, a crotch section and a back waist section of the absorbent article (typically when the absorbent article is a disposable diaper, training pant, adult incontinence garment or feminine hygiene article). The tension in the crotch section of the absorbent core can be reduced by incorporating one or more slits or cuts into the absorbent core. The slits or cuts can be configured to reduce tension experienced during use by the crotch section of the absorbent core. The slit or slits can be oriented in the longitudinal or lateral direction of the absorbent core and can be from about 0.125 inches to about 2 inches depending on the size of the absorbent core and the selected configuration of slits. In another tension reducing geometry, the crotch section of the absorbent core can have a narrower width (or narrower dimension in the lateral direction) than the remainder of the absorbent core.
In another aspect, the continuous elastic absorbent cores of the invention can have a dry tensile strength, and a wet tensile strength that is at least 95% of the dry tensile strength. The tensile strength is a measurement of the force necessary to rupture or break the absorbent core. Typically, the wet tensile strength of an absorbent core is dramatically less than the dry tensile strength-if it is measurable at all (sometimes wet absorbent cores can not even be placed in the measurement device without falling apart). With the elastic absorbent cores of the invention, the wet tensile strength is very close to or even greater than the dry tensile strength.
Additionally, the continuous elastic absorbent cores of the invention can include from about 10 to about 20 weight percent of an elastic material that contributes or imparts the elastic capacity of the absorbent core. More specifically, the continuous elastic absorbent cores of the invention can include from about 13 to about 17 weight percent of an elastic material.
In addition to including continuous elastic absorbent cores, the dynamic-fitting absorbent articles of the invention can include a liquid impermeable outer cover that includes a biaxially stretchable material. A biaxially stretchable material is a material that extends in at least two directions such as the longitudinal and lateral directions of the outer cover and/or the absorbent article. A biaxially stretchable material is a material that is capable of extending upon application of a tensile force, and capable of retracting either partially or close to completely to its original dimension(s) upon removal of the force depending on the desired function of the absorbent article. In another aspect, the absorbent articles of the invention can include a liquid impermeable outer cover that includes a biaxially elastic material. A biaxially elastic material is a material that is capable of extending upon application of a force and that retracts to substantially to its original dimension(s) upon removal of the force. The dynamic-fitting absorbent articles of the invention can further include bodyside liners that include either biaxially stretchable materials and/or biaxially elastic materials. The stretchable and elastic properties of the outer cover and bodyside liner materials can be selected and interchanged depending on the desired function and performance of the absorbent article in conjunction with the absorbent core.
In another aspect, the present invention relates to a dynamic-fitting absorbent article that includes a liquid impermeable, biaxially stretchable outer cover; a liquid permeable, biaxially stretchable bodyside liner; and a continuous elastic absorbent core. The bodyside liner is in superimposed relation to the outer cover and the absorbent core is disposed between the outer cover and the bodyside liner. The continuous elastic absorbent core can extend from about 80 to about 400 percent upon application of a force of from about 60 to about 325 grams. Put differently, the continuous elastic absorbent core has a tension of from about 60 to about 325 grams when the core is extended a percentage, between about 80 and about 400 percent, of its initial length. More specifically, the absorbent core can extend from about 80 to about 400 percent upon a force of from about 100 to about 250 grams. This is the same as the elastic absorbent core having a tension of from about 100 to about 250 grams when the core is extended about 80 percent or any other percentage of its initial length up to about 400 percent. In another aspect, the continuous elastic absorbent core can recover no more than about 80% of an original dimension upon relaxation of the extension force. The original dimension can be in either a longitudinal or a lateral direction. Additionally, the absorbent core has a dry tensile strength and a wet tensile strength that is at least 95% of the dry tensile strength.
The present invention also relates to a dynamic-fitting absorbent article that includes a liquid impermeable outer cover, a liquid permeable bodyside liner and a continuous elastic absorbent core. The bodyside liner is in superimposed relation to the outer cover and the absorbent core is disposed between the outer cover and the bodyside liner. The continuous elastic absorbent core can recover less than about 80% of its original dimension upon relaxation of an extension force. That is to say, when the continuous elastic absorbent core is elongated, the absorbent core does not completely retract when the elongation force is removed. Further, the elastic absorbent core can include less than about 25% of an elastic material.
The elastic absorbent cores of this aspect of the invention are also capable of elongating upon application of a relatively low tension force. For example, the elastic absorbent cores can extend from about 80 to about 400 percent upon application of a force of from about 60 to about 325 grams. More specifically, the elastic absorbent cores can extend from about 80 to about 400 percent upon application of a force of from about 100 to about 250 grams. The benefits associated with form-fitting and body-conforming elastic absorbent cores are typically initially realized upon application of an article because absorbent articles are usually pulled and stretched during application to a wearer. In order to make application of such articles easy, it is desirable for the articles to be stretchable with the application of a low level of force. In order to provide a more comfortable fit to the wearer, it is desirable for the absorbent article to impart low tension during use; for example, it is desirable for the crotch section of the article to impart low tension during wear and loading. Therefore, the elastic absorbent cores of the invention can have a tension-reducing geometry in the crotch section. One example of a tension-reducing geometry is for the absorbent core to have one or more slits (oriented in either the longitudinal or lateral direction). The slits are capable of relieving localized forces and can aid in the distribution of forces across the entire absorbent core. Another tension-reducing geometry is for the elastic absorbent core to have a narrowed width in the crotch section. A narrowed width eliminates surplus material that can potentially bunch-up and pull other components of the article downward.
The continuous elastic absorbent cores of the invention can maintain their xe2x80x9cwetxe2x80x9d integrity and do not massively breakdown during loading or while the article is being worn. Maintenance of the overall integrity of the absorbent core improves the fit of the article during use and contributes to preventing leakage of exudates from the article. Therefore, the elastic absorbent cores can have a dry tensile strength and a wet tensile strength that is at least 95% of the dry tensile strength. Further to the purposes of reducing the tension of the absorbent articles and of not interfering with the absorptive and storage capabilities of the articles, the elastic absorbent cores of the invention have relatively low percentages of elastic materials to impart their flexibility. For example, the continuous elastic absorbent cores can include from about 10 to about 20 weight percent of an elastic material. More specifically, the elastic absorbent cores can include from about 13 to about 17 weight percent of an elastic material.
The articles of the invention can include a variety of outer cover and bodyside liner materials. For example, the outer cover material can have minimal elongation properties, can be stretchable in one or more directions and can be elastic in one or more directions. Similarly, the bodyside liner material can be essentially non-elongatable, can be stretchable in one or more directions and can be elastic in one or more directions. The outer cover and bodyside liner materials can be selected to have elongation properties that are appropriate for the desired function of the absorbent article in which they are used.
To maximize the fit range and conformability of the absorbent articles, it may be desirable for the article to include a liquid impermeable, biaxially stretchable outer cover, a liquid permeable, biaxially stretchable bodyside liner and a continuous elastic absorbent core disposed between the outer cover and the bodyside liner. The biaxially stretchable bodyside liner is in superimposed relation to the biaxially stretchable outer cover. The continuous elastic absorbent core can recover less than about 80% of an original dimension upon relaxation of an extension force and the absorbent core can include less than about 25% of an elastic material. The original dimension of the absorbent core is the length or width of the absorbent core prior to the application of an elongating force. The extension force is typically that force experienced by the absorbent core and the absorbent article during application of the article. The absorbent article desirably can be applied with a minimal effort to xe2x80x9cactivatexe2x80x9d the inherent stretch properties of the article. In order to contribute to the low tension article, the elastic absorbent cores of the invention can extend from about 80 to about 400 percent upon application of a force of from about 60 to about 325 grams. More specifically, the elastic absorbent core can extend from about 80 to about 400 percent upon application of a force of from about 100 to about 250 grams. The continuous elastic absorbent core maintains its integrity after loading (when wet) and can have a dry tensile strength, and can have a wet tensile strength that is at least 95% of the dry tensile strength.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention claimed. The accompanying drawings, that are incorporated in and constitute part of this specification, are included to illustrate and provide a further understanding of the articles and methods of the invention. Together with the description, the drawings serve to explain various aspects of the invention.